During the fabrication of gate-first, MHK devices, patterning of the metal gate high k layers is required. However, the inventors have determined that the gate dielectric can grow significantly during a photoresist removal process. This is clearly undesirable, as the resulting thickness variations can result in the overall geometry and uniformity of the devices being significantly impaired. Additionally, the increased gate dielectric thickness degrades drain currents and also limits gate length scaling.
In US Patent Publication No.: 2005/0136589 A1 a method is shown to pattern high k layers which are present under gate electrode materials. The method consists of standard process steps to deposit a high k layer, next deposit a gate electrode material and then pattern the gate electrode followed by patterning or removal of the high k material from the extensions and source-drain regions out side the patterned gate electrode as a separate step in the patterning of the gate electrode. In this approach it is desired to prevent dielectric re-growth in the lateral direction. Since the high k material can absorb oxygen and move laterally, by eliminating the high k material outside of the gate electrode lateral dielectric re-growth nonuniformity can be reduced.
In US Patent Publication No.: 2006/0246647A1 a method is shown to form separate regions of SiO2 and high k gate dielectrics on the same chip. The method uses a photoresist layer to block regions of high k dielectrics from being removed during a patterning process.
In US Patent Publication No.: 2006/0246651 there is shown a method to remove SiO2 dielectric from an I/O region using a disposable barrier layer to protect the SiO2 from damage during removal. The method is said to also eliminate contamination of the high k material to other components of the chip structure.
In US Patent Publication No.: 20070122962 there is shown a method to pattern high k dielectric regions and SiO2 dielectric regions on a chip structure. The method utilizes a barrier layer to provide protection to the dielectric regions. The barrier layer is a disposable material which is directly in contact with the dielectric.